A series of investigations will be undertaken to determine whether vitamin A or synthetic retinoids administered systemically to experimental animals, can delay or prevent chemical carcinogenesis of two oral mucosal DMBA model systems--hamster buccal pouch and hamster tongue. Retardation of chemical carcinogenesis will be studied histologically, since these model systems are well defined in terms of the sequence of development of dysplasia, carcinoma-in-situ and frank, invasive epidermoid carcinoma. The distribution of retinoids in oral tissues will be studied by radioautography. Possible mechanisms of the action of retinoids in retarding tumor development will be studied by immunologic assays for enhancement of cell-mediated immunity and by biochemical techniques for alterations related to cyclic AMP and the arachidonic acid-prostaglandin system.